Method of plating using a protective coating on an electroplating work support

ABSTRACT

PROTECTION OF PLATING JIGS, BASKETS, PLATING RACKS, CONVEYOR HOOKS AND THE LIKE FROM CHEMICAL ACTION IN A PLATING OPERATION IS ACCOMPLISHED BY COATING THE AFOREMENTIONED APPARATUS WITH A COMPOSITION COMPRISING (1) A POLYMERIC MATERIAL INSOLUBLE IN BOTH WATER AND PLATING SOLUTIONS AND (2) ANTIMONY OXIDE. THIS IS A CONTINUATION OF APPLICATION S.N. 880,993, NOW ABANDONED, FILED NOV. 28, 1969.

United States Patent US. Cl. 20430 6 Claims ABSTRACT OF THE DISCLOSURE Protection of plating jigs, baskets, plating racks, conveyor hooks and the like from chemical action in a plating operation is accomplished by coating the aforementioned apparatus with a composition comprising (1) a polymeric material insoluble in both water and plating solutions and (2) antimony oxide.

This is a continuation of application S.N. 880,993, now abandoned, filed Nov. 28, 1969.

BACKGROUND OF THE INVENTION This invention relates to coatings that are principally intended to protect electroplating jigs, baskets, plating racks, conveyor hooks and the like from the deposition of metals employed in plating baths.

Electroplated plastic articles wherein the plastic substrate is prepared from such synthetic polymeric materials as acrylonitrile-butadiene-styrene copolymers (ABS) and propylene polymers have achieved extensive commercialization in recent years. The electroplating process generally comprises a series of steps wherein the substrate to be treated is consecutively immersed in the following solutions: etching, sensitizing, activating, chemical plating (electroless plating) and thereafter electroplating. In the etching step, the non-conductive substrate is immersed in an acid etching solution, which may comprise a bath of sulfuric acid and chromic oxide, at a temperature higher than room temperature. The etched surface is then sensitized with a readily oxidizable tin salt solution such as a stannous chloride solution which causes tin to be absorbed onto the surface. Alternatively, the sensitizing step may be accomplished with a titanium trichloride solution. The sensitized substrate is then activated by treatment with an aqueous solution of a noble metal salt such as palladium chloride, gold chloride, silver nitrate or the like to form a metallic film. The activated substrate is then subjected to chemical plating (electroless plating) by immersing the substrate in an aqueous plating solution of either a copper salt, a nickel salt or a silver salt together with such other addition agents as Formalin and sodium hypophosphite. After electroless plating, the surface is ready for conventional electroplating with such finish metals as copper, nickel and/ or chromium.

Electroplating operations require tanks or vats for immersing the articles and the articles require suspension devices or hangers which are resistant to chemicals such as the acids and alkalis employed in the various baths. It is known to coat the jigs, hangers and the like with such thermoplastic resins as polyethylene and polyvinyl chloride, which are Widely employed because they are resistant to most chemicals, are inexpensive and readily coat electroplating apparatus. During the plating operation, the

by dipcoating the particular apparatus with a chemically inert resin to insulate and hermetically enclose the appara- ICC tus. However, during the electroplating process, the resin coated jigs may also be plated in whole or in part along with the suspended plastic articles. This undesirable plating not only reduces the useful life of the plating jigs and other apparatus, since they must be replaced by new apparatus, but in addition, the expensive chemicals employed in the various baths are uselessly consumed. The deposition of a metallic coating on the plating jigs also causes exertiion of much labor and etfort for the cleaning, dissolution and removal of the deposit before the: jigs can be reused. Of even more importance is the significant obstacle presented in automating the plating operation.

It is an object of the present invention to provide a coating composition that may be applied to plating jigs and other apparatus of a plating operation subjected to the chemical action of plating solutions. It is a further object of this invention to provide coated plating apparatus such as jigs, baskets, plating racks and conveyor hooks that are resistant to metal deposition from a plating operation. It is still a further object of this invention to provide a method of coating plating jigs and similar apparatus to obtain coated apparatus resistant to the chemical action of plating baths.

These and other objects of the invention are accomplished by providing a coating composition for plating apparatus comprising (1) a polymeric material insoluble in both water and plating solutions and (2) antimony oxide. The weight ratio of the polymeric material to the antimony oxide in the coating composition may vary from about 5% to about 200% based on the Weight of the polymeric material.

DESCRIPTION OF THE INVENTION The polymeric material that may be employed in the coating composition of this invention includes any of the resins conventionally employed as coating materials for plating jigs and the like provided that the material is insoluble in both water and the chemicals employed in the plating bath. Among suitable thermoplastic resins are, for example, polyolefins such as high-density polyethylene, low-density polyethylene, polypropylene, polybutene, and polyisobutylene; polyvinyl halides such as polyvinyl chloride; and polyvinylidene halides such as polyvinylidene chloride.

The amount of antimony oxide added to the resin may vary from about 5 parts to 200 parts by Weight per parts of the resin. Depending upon the particular application, the coating composition of this invention may additionally contain plasticizers and other conventionally em- The invention is further illustrated by the following examples wherein all parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 100 parts of a low-density polyethylene having a melt index of 20 (g./l0 min.) and commercially available from Asahi Dow Chemical Company as M-6520 was mixed with the same amount of finely-divided antimony oxide on a roll mill of 200 C. Thereafter, the blend was compression molded into square plaques having the dimensions 50 mm. by 50 mm. by 3 mm. in thickness.

Thereafter, the plaques were chemically plated according to the following described process. Several plaques were immersed in an acid etching solution consisting of 80% by volume of sulfuric acid, 20% by volume of water and additionally containing 20 grams of chromic oxide per liter of solution, for 10 minutes at 70 C. The specimens were Washed thoroughly with water and dipped into a sensitizing bath of an aqueous solution containing 10 grams per liter of stannous chloride and 40 cc. per liter of concentrated hydrochloric acid, at room temperature for 3 minutes. Again, the plaques wee washed thoroughly with water and then immersed in an activating solution containing 0.2 gram per liter of palladium chloride and 2.5 cc, per liter of concentrated hydrochloric acid, for a period of 2 minutes at room temperature. Prior to chemical (electroless) copper plating, the following two solutions were prepared:

Solution A Grams per liter Copper sulfate 60 Nickel chloride 15 Hydrazine sulfate 45 Solution B Caustic soda 45 Rochelle salt 180 Sodium carbonate 15 Thereafter, the two solutions were mixed and the plaques dipped into the resultant bath at room temperature for 20 minutes in an attempt to effect a continuous copper coating capable of conducting electricity. However, there was no evidence of copper deposition on the plaques and therefore, of the area of the plaques are chemically plated.

A melt from the coating composition of Example 1 was prepared by heating to 160 C. and then the melt was employed to coat electroplating jigs. The same plating procedure from the conditioning step through the chemical (electroless) plating step was repeated and results were similar to those obtained using the compression molded plaques.

EXAMPLE 2 The procedure of Example 1 for preparing compression molded plaques was repeated except that the amount of antimony trioxide was reduced to 50 parts while still employing 100 parts of the same polyethylene. The plaques were treated by the same chemical plating process described in Example 1 and upon completion of the electroless copper plating step, it was observed that an average of of the area of the plaques were covered with the copper deposit.

Using the same procedure employed in Example 1, a melt of the coating composition was formed by heating to 160 C. and the melt was used to coat electroplating jigs. In a subsequent plating run, the amount of copper deposit on the electroplating jigs corresponded with that amount covering the plaques.

EXAMPLE 3 Again the procedure of Example 1 for preparing a compression molded plaque was repeated with the exception that 20 parts of antimony trioxide were employed together with 100 parts of the polyethylene of Example 1.

The plaques were treated to the same plating process described in Example 1 and after completion of the electroless copper plating step, it was observed that an average of 60% of the area of the plaques were covered with a copper deposit.

A melt was prepared by heating the composition of Example 3 to 160 C. and the melt was applied to electroplating jigs. When the jigs were used in a subsequent electroplating run, approximately 60% of the area of the jigs were covered with a copper deposit.

EXAMPLE 4 Following the procedure of Example 1, 20 parts of finely-divided antimony trioxide was blended with parts of a crystalline polypropylene, commercially available from Chisso Corporation as Chisso Polypro 1008, and having a melt flow rate of 9.5 (grams/ 10 min). Molded plaques were prepared from the blend.

The same plating procedure of Example 1 Was repeated using the aforementioned plaques, and upon completion of the electroless plating step, it Was observed that an average of 20% of the area of the plaques were covered with the copper deposit.

A melt was prepared by heating the polypropylene composition to 220 C. and the melt was applied to electroplating jigs. When the coated jigs Were employed in an electroplating run, approximately 20% of the surface of the jigs were coated with the copper deposit.

EXAMPLE 5 Following the procedure in Example 1, plaques were molded from a blend of 100 parts of polyvinyl chloride having a degree of polymerization of 650 (commercially available from Chisso Corporation as Nipolit SK, 20 parts of dioctyl phthalate, and 50 parts of antimony trioxide.

The same plating procedure described in Example 1 was repeated using the aforementioned plaques and upon completion of the electroless plating step, it was observed that there was an absence of a copper deposit on the surface of the plaques, and therefore, the portion of the plaques considered plated was 0%.

A melt was formed from the aforementioned coating composition by heating to C. and the melt was used to coat electroplating jigs. The coated jigs were employed in an electroplating run and again there was no metallic deposit on the jigs.

For purposes of comparison, the following controls are presented to further illustrate the advantages of the invention:

Control A Control B The procedure of Example 4 was repeated with the exception that the antimony trioxide was omitted. Molded plaques were treated according to the plating process described in Example 1 and after completion of this process, it was observed that 100% of the area of the plaques were covered with the copper deposit.

Control C The procedure of Example 5 was repeated with the exception that antimony trioxide was not employed. After treating the plaques to the plating process described in Example 1, it was observed that the metallic deposit covered the entire surface area (100%) of the plaques.

What is claimed is:

1. In an electroplating process wherein an article to be plated is supported on a support and conveyed consecutively through aqueous etching, sensitizing, activating, chemical plating, and electroplating solutions, the improvement comprising having a plating solution, resistant coating on said support, said coating comprising (1) a synthetic, organic, thermoplastic polymeric material insoluble in both water and said solutions, and (2) antimony oxide.

2. The process of claim 1 wherein said polymeric material is a thermoplastic polymer selected from the group consisting of polyolefins, polyvinyl halides and polyvinylidene halides.

3. The process of claim 1 wherein said polymeric material is polyethylene.

4. The process of claim 1 wherein said polymeric material is polypropylene.

5. The process of claim 1 wherein said polymeric material is polyvinyl chloride.

6. The process of claim 1 wherein said antimony oxide is employed in an amount from 15 to 100 parts by weight per 100 parts of said polymeric material.

References Cited UNITED JOHN H. MACK, Primary Examiner 10 R. J. FAY, Assistant Examiner US. Cl. X.R. 

